Hot-water extraction and characterization of spruce bark non-cellulosic polysaccharides Myriam Le Normand, Ulrica Edlund, Bjarne Holmbom and Monica Ek KEYWORDS: Bark, Biorefinery, Hemicelluloses, Norway spruce, Pectins SUMMARY: Non-cellulosic polysaccharides (NCP) from bark offer large potential as a class of natural raw materials for functional materials development and production of biochemicals. We have elaborated a process for sequential extraction of NCP from industrial Norway spruce bark using an accelerated solvent extraction (ASE) with water at 100 to 160°C. Carbohydrates, Klason lignin and ash content as well as size-exclusion chromatography (SEC) analyses were performed for all hot-water extracts. NCP were mainly composed of glucose, arabinose and galacturonic acid units which revealed the presence of starch, arabinose-rich hemicelluloses and pectins. In total, the industrial bark of Norway spruce contained up to 20% of NCP which were extracted with pressurized hot water. NCP were mainly extractable at 140°C and started to undergo degradation at higher temperature. ADDRESSES OF THE AUTHORS: Myriam Le Normand (myriamln@kth.se) and Monica Ek (monicaek@kth.se): Division of Wood Chemistry and Pulp Technology, Department of Fiber and Polymer Technology, Royal Institute of Technology, KTH, Teknikringen 56, SE-100 44 Stockholm, Sweden. Ulrica Edlund (edlund@polymer.kth.se): Division of Polymer Technology, Department of Fiber and Polymer Technology, Royal Institute of Technology, KTH, Teknikringen 56, SE-100 44 Stockholm, Sweden. Bjarne Holmbom (bholmbom@abo.fi): Process Chemistry Centre, Laboratory of Wood and Paper Chemistry Åbo Akademi University, FI-20 500 Turku/Åbo, Finland Corresponding author : Monica Ek Norway spruce (Picea abies) represents 45% of the total forest area in Sweden and is together with Scots pine the most important raw material for Scandinavian timber and paper industry. The annual national consumption of spruce in Sweden is about 43 million m 3 (Loman 2010). Considering that the bark represents approximately 10% of the tree and that the density of dry bark is around 350 kg m-3, then an estimation of the industrial processing of spruce in Sweden would annually give 1.5 million tons of bark (dry weight). Today, these considerable amounts of biomass are mostly disregarded and used as fuel to process heat and electrical energy in the mills. However, efficient exploitation of this abundant by-product could create new industries, novel applications and a wide range of value-added substances. This strategy can be included in a bark biorefinery concept similar to the one illustrated in Fig 1. The bark biorefinery plant might be built close to an existing mill and exploit part of the wet bark stream coming directly after the debarking process. Fractionation of high-value compounds might be performed inside the biorefinery and its residues could be redirected to the bark boiler. In order to find new applications for spruce bark, fundamental knowledge about the chemistry of the bark is of importance. Bark components which have the potential of being exploitable are tannins for their adhesive properties (Roffael et al. 2000; Kylliäinen, Holmbom 2004; Zhang, Gellerstedt 2009), specialty chemicals due to their potential bioactivity (Pietarinen et al. 2006; Co et al. 2011; Nilsson 2011), polysaccharides for biofuel production (Hu et al. 2008) or also as a source of natural biopolymers for designing renewable materials such as hydrogels (Voepel et al. 2009) or films (Edlund et al. 2010; Mikkonen et al. 2010). Carbohydrates usually found in woody biomasses include cellulose, hemicelluloses, starch and pectins. The non-cellulosic polysaccharide (NCP) fraction constitutes 20−30% of the raw material and can be extracted by pressurized hot water. Hot-water treatment is attractive since it combines high extraction yields with an environmentally friendly process. The accelerated solvent extraction (ASE) system used in this study allowed automated and reproducible extraction conditions and has already been used for sequential extraction and characterization of Norway spruce NCP (Song et al. 2011). Contrary to Norway spruce wood, very few reports have presented the carbohydrate composition of the bark. Schädel et al. (2010) extracted hemicelluloses from different plant species by micro-extraction and showed that bark from softwoods contained approximately 10% (dry mass) of non-starch and non-cellulosic polysaccharides. Nevertheless, they did not report the exact carbohydrate composition of Norway spruce bark. In a recent study, we focused on the carbohydrates in fresh inner bark of Norway spruce, and more precisely on the NCP fraction (Le Normand et al. 2010). The study was limited to inner bark since it exhibited the most important source of carbohydrates. In parallel to our work, Krogell et al.(2012) presented the overall composition of Norway spruce inner and outer Fig 1. Proposed bark biorefinery concept. BIOREFINARY 18 Nordic Pulp and Paper Research Journal Vol 27 no.1/2012 Brought to you by | Lund University Libraries Authenticated Download Date | 11/22/18 4:05 PM